The present invention relates to the amplification of optical signals in long-haul optical communications systems.
In optical transmission systems, both incoming and outgoing signals are amplified at the line terminal equipment (LTE) to ensure adequate signal strength. Optical amplifiers, such as erbium-doped fibre amplifiers (EDFAs), are now in widespread use to achieve this aim. When the optical signal passes through an EDFA a pump is applied at a wavelength which causes excitement of the erbium atoms in such a way that there is consequent amplification of the optical signal. Suitable lasers for the task are widely available, and are conventionally provided with integrated control electronics.
Traditionally, when designing high-reliability optical amplifiers for use in submarine LTEs, the pump lasers and their associated electronics are duplicated to provide redundancy should one fail. They are also replaceable. Since they are integrated, failure of either a pump or of its control electronics requires replacement of both. As the pump laser must clearly be optically connected to the EDFA, this requires optical fibres to be disconnected creating a potential safety hazard.